Since updating to macOS Sierra, many Finder aliases appear as generic document icons rather than as the informative icons that were available in previous versions of OS X.
Is there something I can do to fix this?
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Do a "Get Info" on the alias, and you should see that the correct icon is displayed at the top left of the Get Info window. Copy the icon and paste it back. When the window is closed, the correct icon should appear in the Finder window. This should survive a reboot. Once the icon has been pasted back in, the size of the alias should grow larger.